How long before I have to move out of my apartment when I'm two months behind in rent

I am not certain that I understand your question. Presumably, the lease agreement allows the landlord to terminate lease if you do not timely pay. That has occurred. The landlord cannot physically move you out. But the landlord could file a lawsuit for eviction and have the court order you to leave. That usually takes months.

Nonpayment of rent is one of (if not the) most common reasons for eviction actions starting. I would look at your lease regarding what length of notice the Landlord has to give you. If it does not specify the length of notice in the lease, then look to Wis. Stat Chapter 704. If the lease is for one year or less, they may serve you with a 5 day notice with right to cure. If the lease is for longer than a year, the notice has to be a 30 day with right to cure.